1. Field of the Invention
The present invention relates to a recording-reproducing apparatus for recording by employing electromagnetic wave irradiation arid electric field application and reproducing by detecting a tunnel current, and a recording-reproducing method employing the apparatus. And the present invention relates to further a novel recording medium used suitably for the recording and reproducing method.
2. Related Background Art
Applications of memory materials are the most important field of electronic industries such as computors and related apparatus, video-disks, and digital audio-disks. The developement of the materials are the subject of comprehensive studies in recent years. Although the performances required to the memory materials depend on the application fields thereof, the generally required performances are as below:
(1) High recording density and large recording capacity,
(2) High response speed of recording and reproduction,
(3) Low electric power consumption, and
(4) High productivity and low cost. and so forth.
Heretofore, semiconductor memories and magnetic memories based on a semiconductor or a magnetic substance are predominantly used for memory materials. Lately as a result of the progress of laser technology, low-cost and high-density recording media have been developed employing an optical memory by use of an organic thin film of an organic coloring matter, a photopolymer, etc.
On the other hand, the scanning tunnelling microscope (hereinafter referred to as STM) has been recently developted to enable a direct observation of an electronic structure of surface atoms or molecules of a conductor with a resolving power of 0.1 nm [G. Binnig et al., Phys. Rev. Lett. 49 (1982) 57]. Recently, by using STM, an experiment has been conducted in which a pulse voltage is applied between a probe electrode and an electroconductive material to fabricate locally the surface of the electroconductive material and the change of the shape or state of the surface is read [J. S. Foster et al., Nature 331 (1988) 324]. Further by means of the STM, switching characteristics and rectification characteristics of an organic molecule have been investigated [A. Aviram et al., Chem. Phys. Lett. 146 (1988), 490].
However, even with the highest density and the largest recording capacity of the conventional optical memories practically used, the recording capacity is at most 10.sup.8 bit/cm , which is becoming insufficient to the image recording in modern computors and video apparatuses.
The recording and reproduction by use of STM, although the recording can be conducted with a bit size in the order of an interatomic or intermolecule distance (0.5 to 50 nm), is not satisfactory from the viewpoint of the reproductivity and stability, and yet its recording and erasing mechanism has not been elucidated. Moreover, in measurement of electric characteristics by accessing a molecule by means of STM, the record may sometimes be affected by reproducing operation (voltage application) because recording and reproduction are made by voltage application. Therefore STM is not satisfactory for application to memory.